Merge feat/sqlite-migration: add database schema migration system

This merge brings the SQLite migration system from feat/sqlite-migration branch:

## New Features
- Schema version control with SCHEMA_VERSION constant
- Automatic migration of missing columns for providers table
- Dry-run validation mode for schema compatibility checks
- JSON→SQLite migration feature gate (CC_SWITCH_ENABLE_JSON_DB_MIGRATION)
- Settings reload mechanism after imports

## Test Updates
- Updated tests to use SQLite database instead of config.json
- Removed obsolete import_config_from_path tests (replaced by db.import_sql)
- Fixed MCP tests to use unified McpServer structure (v3.7.0+)
- Updated provider switch tests to reflect no-backfill behavior
- Adjusted error type matching for new error variants

src-tauri/src/lib.rs

@@ -113,6 +113,25 @@ const TRAY_SECTIONS: [TrayAppSection; 3] = [
     },
 ];
 
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+enum JsonMigrationMode {
+    Disabled,
+    DryRun,
+    Enabled,
+}
+
+/// 解析 JSON→DB 迁移模式：默认关闭，支持 dryrun/模拟演练
+fn json_migration_mode() -> JsonMigrationMode {
+    match std::env::var("CC_SWITCH_ENABLE_JSON_DB_MIGRATION") {
+        Ok(val) => match val.trim().to_ascii_lowercase().as_str() {
+            "1" | "true" | "yes" | "on" => JsonMigrationMode::Enabled,
+            "dryrun" | "dry-run" | "simulate" | "sim" => JsonMigrationMode::DryRun,
+            _ => JsonMigrationMode::Disabled,
+        },
+        Err(_) => JsonMigrationMode::Disabled,
+    }
+}
+
 fn append_provider_section<'a>(
     app: &'a tauri::AppHandle,
     mut menu_builder: MenuBuilder<'a, tauri::Wry, tauri::AppHandle<tauri::Wry>>,
@@ -542,8 +561,10 @@ pub fn run() {
             let db_path = app_config_dir.join("cc-switch.db");
             let json_path = app_config_dir.join("config.json");
 
-            // Check if migration is needed (DB doesn't exist but JSON does)
-            let migration_needed = !db_path.exists() && json_path.exists();
+            // Check if config.json→SQLite migration needed (feature gated, disabled by default)
+            let migration_mode = json_migration_mode();
+            let has_json = json_path.exists();
+            let has_db = db_path.exists();
 
             let db = match crate::database::Database::init() {
                 Ok(db) => Arc::new(db),
@@ -555,19 +576,42 @@ pub fn run() {
                 }
             };
 
-            if migration_needed {
-                log::info!("Starting migration from config.json to SQLite...");
-                match crate::app_config::MultiAppConfig::load() {
-                    Ok(config) => {
-                        if let Err(e) = db.migrate_from_json(&config) {
-                            log::error!("Migration failed: {e}");
-                        } else {
-                            log::info!("Migration successful");
-                            // Optional: Rename config.json
-                            // let _ = std::fs::rename(&json_path, json_path.with_extension("json.bak"));
+            if !has_db && has_json {
+                match migration_mode {
+                    JsonMigrationMode::Disabled => {
+                        log::warn!(
+                            "Detected config.json but migration is disabled by default. \
+                             Set CC_SWITCH_ENABLE_JSON_DB_MIGRATION=1 to migrate, or =dryrun to validate first."
+                        );
+                    }
+                    JsonMigrationMode::DryRun => {
+                        log::info!("Running migration dry-run (validation only, no disk writes)");
+                        match crate::app_config::MultiAppConfig::load() {
+                            Ok(config) => {
+                                if let Err(e) = crate::database::Database::migrate_from_json_dry_run(&config) {
+                                    log::error!("Migration dry-run failed: {e}");
+                                } else {
+                                    log::info!("Migration dry-run succeeded (no database written)");
+                                }
+                            }
+                            Err(e) => log::error!("Failed to load config.json for dry-run: {e}"),
+                        }
+                    }
+                    JsonMigrationMode::Enabled => {
+                        log::info!("Starting migration from config.json to SQLite (user opt-in)");
+                        match crate::app_config::MultiAppConfig::load() {
+                            Ok(config) => {
+                                if let Err(e) = db.migrate_from_json(&config) {
+                                    log::error!("Migration failed: {e}");
+                                } else {
+                                    log::info!("Migration successful");
+                                    // Optional: Rename config.json to prevent re-migration
+                                    // let _ = std::fs::rename(&json_path, json_path.with_extension("json.migrated"));
+                                }
+                            }
+                            Err(e) => log::error!("Failed to load config.json for migration: {e}"),
                         }
                     }
-                    Err(e) => log::error!("Failed to load config.json for migration: {e}"),
                 }
             }